Research on DC Bus Floating On-Board Charger Based on CLLLC Converter Segment Modulation

With the continuous improvement of electric vehicle charging technology, the voltage range of its power battery is widening, and the optimal design of on-board charger (OBC) has become an important link in the development of the electric vehicle industry. In this paper, based on the new OBC topology, aiming at the problem of low efficiency when the latter bidirectional CLLLC resonant converter adopts frequency conversion modulation to step down, a segmented hybrid modulation strategy of frequency conversion and extended phase shift (EPS) based on variable DC bus voltage control is proposed to achieve OBC wide voltage gain and high-efficiency control objectives. Frequency conversion modulation is adopted when the gain <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$m$</tex> is more than or equal to 1; When the gain <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$M&lt;1$</tex>, the extended phase shift modulation is adopted, and the step-down range of OBC is widened by the phase shift in the primary side bridge and the phase shift between the primary and secondary side bridges. Finally, an experimental prototype with 220 Vac input and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$250 \sim 750 \text{Vdc} / 6.6 ~\text{kW}$</tex> output was built to verify the effectiveness of the proposed control strategy.